i tried this mod on my last car (vectra) , it is not easy to do and all you end up with is two knackered keys
you have to hack away inside the flip key so that the pcb fits inside (easy to do)
you also have to cut the flip key buttons , because when they are depressed they have a black plastic bit that pushes down onto the switch , these need shortening so that you can glue the micro switches to the fob housing ( one false move here and cut the plastic things to short and your flip key is u/s)
you then have to run wires from the micro switches that you removed from your perfectly good fob to your good pcb and then try to reassemble the flip key ( and because you have to cut the fob open in the first place you are never going to get it together properly)
please bear in mind that the seal on the flip key will never be brilliant and inside you will have to put the chip from your key to enable you to start the car :-/
having tried this mod all i can say is I REALLY RECCOMEND YOU DONT DO IT unless you have money to buy yourself a new spare key

This is a link to the site i got info from
http://www.yellowdawg.co.uk/flipkey/Untitled-1.html